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Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-02.txt

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Sat, 25 October 2014 20:16 UTC

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Date: Sat, 25 Oct 2014 23:16:42 +0300
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Watson Ladd <watsonbladd@gmail.com>
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Subject: Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-02.txt
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On Sat, Oct 25, 2014 at 12:55:58PM -0700, Watson Ladd wrote:
> On Sat, Oct 25, 2014 at 12:51 PM, Nikos Mavrogiannopoulos
> <nmav@redhat.com> wrote:
>
> > 3. There are known attacks against the current ServerKeyExchange format which
> > remain applicable if we go this path (a sufficiently long DH serverkeyexchange
> > message can be parsed as an ECDH serverkeyexchage).
> 
> And 4: session_hash solves the same problem if I understand the
> elements of it correctly, and we need it anyway because of this
> ambiguity in parsing mentioned above. So do we even need this draft?

AFAIK, no, it won't, at least not completely.

(TLS 1.3 has this problem fixed, even without session_hash[1]).


[1] Without session_hash TLS 1.3 is broken in other ways without DH
order check (and one can't rely on endpoints to perform such check
even if it is feasible, so session_hash is a good idea there too).


-Ilari

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